The invention relates to a 4/3 to 16/9 TV format conversion process. It also relates to a converter for the implementation of this process.
Usual 4/3-to-16/9 TV format conversion can be achieved in different ways. FIG. 1a shows a frame of a virtual scene generated by a 4/3 camera and FIG. 1b one generated by a 16/9 camera.
FIG. 2 illustrates known ways to convert a 4/3 TV format to a 16/9 TV format:
The simplest method consists of keeping the 4/3 format and filling the empty parts of the 16/9 frame by black bands, as shown on FIG. 2a. 
Another type of methods consists of distorting or cutting the 4/3 source frame in order to obtain a 16/9 frame:
horizontal zoom which horizontally extends the 4/3 frame (FIG. 2b)
zoom and cutting of the high and low parts of the frame (FIG. 2c)
the same zoom, but only the high part of the frame is cut in order to keep the sub-titles (FIG. 2d)
linear zoom, that is the zoom factor varying in the frame; near to 1 on the center, it takes its maximum values near the frame borders (FIG. 2e).
A compromise between these methods may also be used.
A last type of methods aims at creating the missing information on the borders by specific techniques:
duplication of the border rows or lines
mirror effect (FIG. 2f)
padding methods, adapted deformations taking into account the objects edges, fractals . . .
These different methods can be applied either directly on the TV set or before the video broadcasting in a post-production process. It is clear that these techniques do not allow to create the true information, that is the entire frame of the scene filmed by a 16/9 camera, even if they are achieved in post-production.
All theses techniques deteriorate the overall image quality by adding false information (this added information not representing the actual missing part of the image), by suppressing information or by distorting the image when using information intrinsic to the 4/3 format image.
The object of the invention is to overcome the aforementioned drawbacks.
To this end, the subject of the invention is a format conversion process for a video sequence made up of a succession of frames with a given format to convert these frames into frames with a larger format, characterized in that
it carries out a motion estimation of the current frame relatively to a previous extended view,
it compensates in motion the previous extended view relatively to the current frame,
it updates the previous extended view by taking into account data from the current frame to give an updated extended view becoming the previous extended view for the motion estimation of the next current frame,
it completes the current frame with data from the up-dated extended view to provide the frame with a larger format.
Another subject of the present invention is a format conversion process for a video sequence made up of a succession of frames of a given format to convert these frames into frames with a larger format, characterized in that this conversion is carried out in two passes, one to estimate the motion between successive frames and to built an extended view of the sequence with the frames compensated in motion, the other by positioning each frame of the sequence relatively to the extended view by taking into account the calculated motion and by completing it with extended view data corresponding to the larger format.
According to a particular aspect of the invention, the process is characterized in that the motion estimation is a global motion robust estimation based on an affine modelization of the 2D apparent motion.
According to another particular aspect of the invention, the process is characterized in that the motion estimation is based on the spatio-temporal gradients of the frame luminance.
The invention also relates to a 16/9 television set characterized in that it comprises a converter implementing the format conversion process.
This invention aims at generating a full 16/9 frame from a 4/3 format frame by using an extended view memory built from successive frames of the video plan.
The claimed extended view generation process consists of accumulating successive 4/3 frames and mixing them to produce a bigger one, ideally at the 16/9 format or more. If the camera and the scene background are totally static, this process will produce a final frame with exactly the same size as the 4/3 frame. But as soon as the camera moves (and especially when a panning motion is applied), a larger part of the scene is seen through the successive frames of the video plan, and hence it is possible to produce a larger frame of the scene. If this larger frame is stored in an extended view memory, the 4/3 frame can be completed by this extended view to produce the 16/9 frame of the scene as if it was seen by a 16/9 camera.
Reconstructing the missing parts of the 16/9 frame by using an extended view memory built from successive frames of the video plan allows to get 16/9 frames without distortion or false information, increasing the image quality.